1. Field of the Invention
The present invention relates to an exhaust gas heat exchanger for a cogeneration system, and, more particularly, to an exhaust gas heat exchanger for a cogeneration system which not only achieves an enhancement in the efficiency of heat exchanger between exhaust gas and a heat medium, but also has a compact structure.
2. Description of the Related Art
In general, cogeneration systems are adapted to generate both electricity and heat from a single energy source.
Such a cogeneration system can recover heat of exhaust gas or waste heat of cooling water generated from an engine or turbine during an electricity generation operation, so that the cogeneration system can achieve an increase in energy efficiency of 70 to 80% over other systems. By virtue of such an advantage, the cogeneration system has recently been highlighted as an electricity and heat supply source for buildings. In particular, the cogeneration system exhibits highly-efficient energy utilization in that the recovered waste heat is mainly used to heat/cool a confined space and to heat water.
FIG. 1 is a schematic view illustrating a configuration of a conventional cogeneration system which is used for a cooling and heating apparatus.
As shown in FIG. 1, the conventional cogeneration system include an engine 1 to which fuel is supplied, a generator 3 which is driven to generate electricity, a cooling water heat exchanger 5 which recovers heat from cooling water used to cool the engine 1, and an exhaust gas heat exchanger 9 which is arranged at an exhaust gas discharge conduit 7 extending from the engine 1 to recover heat from exhaust gas discharged from the engine 1. The cogeneration system also includes a heat transfer line which transfers the recovered cooling water heat and exhaust gas heat to a cooling and heating apparatus 20.
The electricity generated from the generator 3 is used to operate various electronic appliances including the cooling and heating apparatus 20 and illumination devices.
The waste heat generated from the engine 1, that is, the heat generated from the cooling water used to cool the engine 1 and the heat generated from the exhaust gas discharged from the engine 1, is used in the cooling and heating apparatus 20 during a heating operation of the cooling and heating apparatus 20, and is outwardly discharged during a cooling operation of the cooling and heating apparatus 20. In order to outwardly discharge the waste heat generated from the engine 1 during the cooling operation of the cooling and heating apparatus 20, the cogeneration system also includes a radiator 17 which includes a heat exchanger 15 and a radiating fan 16.
The cooling and heating apparatus 20 is of a heat pump type so that it is used not only as a cooling apparatus, but also as a heating apparatus, in accordance with reversal of a refrigerant flow in a refrigerant cycle in the cooling and heating apparatus 20. As in a typical heat pump type cooling and heating apparatus, the cooling and heating apparatus 20 includes a compressor 21, a 4-way valve 23, an outdoor heat exchanger 25, an outdoor fan 26, an expansion device 27, and an indoor heat exchanger 29.
An air pre-heating heat exchanger 30 is arranged near the outdoor heat exchanger 25 in order to pre-heat air supplied toward the outdoor heat exchanger 25, using the waste heat of the engine 1.
The air pre-heating heat exchanger 30 is connected to the cooling water heat exchanger 5 and exhaust gas heat exchanger 9 via the heat transfer line 11.
Meanwhile, the exhaust gas heat exchanger 9 includes a shell 31 arranged in the exhaust gas discharge conduit 7 such that exhaust gas introduced into the exhaust gas discharge conduit 7 passes through the shell 31, and a heat medium tube 32 arranged in the shell 31. A heat medium is circulated through the heat medium tube 32.
Hereinafter, operation of the conventional cogeneration system having the above-mentioned configuration will be described.
First, exhaust gas discharged from the engine 1 during the heating operation of the cooling and heating apparatus 20 is introduced into the shell 31 of the exhaust gas heat exchanger 9, and passes through the shell 31.
The exhaust gas transfers heat to the heat medium flowing through the heat medium tube 32 while passing through the shell 31. The heat medium flows to the air pre-heating heat exchanger 30 after absorbing the heat of the exhaust gas, and pre-heats outdoor air in the air-preheating heat exchanger 30.
The pre-heated air is supplied to the outdoor heat exchanger 25, and heat-exchanges with the outdoor heat exchanger 25. Since the pre-heated air is supplied to the outdoor heat exchanger 25, it is possible to prevent a degradation in the heating capacity of the heat pump, which may be caused by a low outdoor air temperature.
Meanwhile, it is unnecessary to supply the recovered waste heat to the cooling and heating apparatus 20 during the cooling operation of the cooling and heating apparatus 20. In this case, accordingly, the flow path of the heat medium is changed to be connected to a radiating line 13, which is connected to the heat transfer line 11, in order to outwardly discharge the recovered waste heat through the radiator 17, or to supply the recovered waste heat to another system such as a hot water supplying apparatus.
In FIG. 1, reference character “P” designates pumps respectively adapted to pump the heat medium such that the heat medium is circulated through desired lines, and reference character “V” designates a valve adapted to change the flow path of the heat medium between the heat transfer line 11 and the radiating line 13.
In the above-mentioned conventional cogeneration system, however, there is a problem in that it is necessary to increase the size of the exhaust gas heat exchanger for an enhancement in efficiency because the exhaust gas heat exchanger includes the shell, through which exhaust gas passes, and the heat medium tube, through which the heat medium passes.